This project investigates how rhesus monkeys and other nonhuman primate species born and raised under different laboratory conditions adapt to placement into environments that contain specific physical and social features of the monkey's natural habitat. Adaptation is assessed by examining behavioral repertoires and by monitoring a variety of physiological systems in these subjects, yielding broad-based indices of relative physical and psychological well-being. The responses of subjects to experimental manipulation of selected features of their respective environments are also assessed in similar fashion. Whenever possible, field data are collected for appropriate comparisons. An additional focus is on investigating the cognitive, behavioral, and social processes involved in adaptation to new settings or circumstances. Capuchin monkeys are employed in many of these studies because they are unique among monkeys species in their propensity to manufacture and use tools to modify their physical environment. Research carried out during FY00 (a) documented a predictive relationship between individual differences in maternal care received by rhesus monkey infants and their subsequent distress exhibited following the birth of a younger sibling in a wild-living rhesus monkey population on Cayo Santiago island (PR); (b) characterized individual differences in the form and amount of infant-directed aggression and other aspects of maternal behavior among rhesus monkey mothers living in the LCE's 5-acre field enclosure at the NIHAC; (c) identified differences between abusive behavior by mothers directed toward their offspring and aggressive behavior directed toward other members of their social group; (d) documented instances of kidnapping of rhesus monkey infants by nonkin juvenile and adult females and related such behavior to differences in social rank between the infants' mothers and their kidnappers; (e) characterized individual differences in alloparenting behaviors toward infants by adult male rhesus monkeys living in the 5-acre field enclosure as a function of the infants' gender and their mothers' age, social rank, and previous maternal experience;(f) characterized the development of social grooming patterns and conflict resolution over the second and third year of life in monkeys reared in the absence of adults; and (g) characterized changes in steroid hormone secretion associated the introduction of contraceptives in adult female capuchin monkeys.